Suicide rates in Europe vary widely, with countries such as Spain, Italy
and Greece reporting rates below 7 per 100 000 inhabitants per year, whereas
others such as Hungary and Finland report rates in excess of 27 per 100 000
inhabitants per year (World Health
Organization, 1994). In addition, since the break-up of the
Yugoslav and the Soviet Federations it has become apparent that newly
independent countries such as Estonia, Latvia, Lithuania and Slovenia also
have high rates of suicide (Table
1).

RISK FACTORS

Risk factors for suicide are traditionally divided into medical (e.g.
mental disorders), psychosocial (e.g. divorce), cultural (e.g. lack of
religious commitment) and socio-economic (e.g. unemployment). At first sight
it seems plausible that sociocultural factors should be the major causes of
different suicide rates across Europe. However, such a thesis fails to hold up
under closer scrutiny. A more promising method for identifying risk factors
for suicide is to consider that they are composed of genetic and environmental
influences.

Although scant, recent research findings support a role for genetic risk
factors for suicide (Roy et al,
1999). An association between positive family history and risk of
suicide by violent means has been reported
(Linkowski et al,
1985), and a large community twin study has shown that genetic
risk factors accounted for approximately 45% of the variance in suicidal
thoughts and behaviour (Statham et
al, 1998). Adoption studies also have shown increased rates
of suicide in the biological rather than adopting relatives of adoptees
(Wender et al,
1986).

Suicide is frequently associated with mental disorder, suggesting the
possibility of shared susceptibility factors, and recent molecular genetic
studies have focused on serotonin transmission and suicidal ideation. An
association has been found between a tryptophan hydroxylase (TPH) polymorphism
and suicidal ideation, the severity of the suicide attempt and alcoholism
(Nielsen et al, 1998).
Also, Mann et al
(1997) have reported positive
associations with the same polymorphism among suicide-attempting depressed
patients.

This evidence suggests an important role for genetic factors in suicidal
behaviour. Could genetic differences, at least in part, account for the
varying rates of suicide in Europe, for example genetic and environmental risk
factors acting additively under a multi-factorial polygenic mode of
inheritance? First, we will argue that it is not possible to explain the
differences in suicide rates across Europe by sociocultural differences alone.
Second, we will explore the case for shared genetic risk factors influencing
the rates of suicide in high-risk European countries, using evidence from
population genetics. Third, we will speculate on the role of possible
interactions between exposure to alcohol and genetic vulnerability.

SOCIOCULTURAL FACTORS: SLOVENIA AS A ‘BLACK SWAN’

Part of the variation in suicide rates across Europe could be due to
different practices in the recording of cause of death. However, most
contemporary researchers now agree that these errors are randomised, at least
to the extent that allows valid cross-national comparison
(Diekstra, 1993). If the
variation in European suicide rates reflects genuine differences, we can argue
that Slovenia provides in the Popperian sense a ‘black swan’ that
refutes conventional predictions. (Popper argued that the appropriate test of
the hypothesis ‘all swans are white’ was to attempt refutation by
finding a black swan.) According to psychosocial predictors, Slovenia should
share the same low rate with its Mediterranean neighbours such as Italy. Also,
about 70% of its population are Roman Catholic - a religion where suicide is
strictly forbidden. However, Slovenia has a high suicide rate of 31 per 100
000 per year. Also, the annual suicide rate in Slovenia has remained
remarkably stable
(Marušič,
1999), despite recent profound political and social change.
According to sociological theories, such changes should have led to yearly
variations in the Slovenian suicide rate
(Diekstra, 1993). Moreover,
high rates of suicide in the native rather than the immigrant population
(Marušič,
1999) also contradict the theory that social and ecological risk
factors are the major influence on suicide statistics.

POPULATION GENETICS AND SUICIDE RATES

This suggests that factors other than environmental stressors alone may be
implicit in determining the high suicide rate in Slovenia and other high-rate
countries. Such factors could include genetic predisposition and some shared
genetic vulnerability between neighbouring populations, for example between
Slovenia and Hungary. An example of shared genetic predisposition can be found
in the Hungarians in central Europe and the Finns and Karelians in the north,
who belong to the same ethnic group (Finno-Ugrians). Both Hungary and Finland
report high suicide rates (Table
1) and other members of this ethnic group elsewhere in Europe also
have high suicide rates, for example in Sweden and the Urals. It has been
suggested that high suicide rates in Finno-Ugrians
(Kondrichin, 1995) could be due
to the fixation in the gene pool of certain behavioural traits predisposing to
suicide during the early stages of ethnogenesis. It is also noteworthy that
both Finns and Hungarians share the same proportion of European (90%) to
Uralic (10%) genes (Cavalli-Sforza et
al, 1994).

More detailed national suicide data now are available following the
emergence of the new Republics after the break-up of Yugoslavia and the Soviet
Union. It is possible now to link nations with high suicide rates along a
J-shaped curve from Finland to Austria, identified in
Fig. 1 by shading those
European countries with rates above 20 per 100 000 per year. This J-curve
pattern also supports the thesis that genetic predisposition could have
influenced the suicide rates in these neighbouring countries. In addition, now
that new data are available for the Baltic States indicating that these
countries also have high suicide rates
(Table 1), it is possible that
the people in these neighbouring countries may share similar proportions of
Uralic genes to those of the Finns and Hungarians.

GENETIC CONSTITUTION AND EXPOSURE TO ALCOHOL: A MALIGNANT
INTERACTION

Another aspect of possible genetic risk factors for suicide relates to the
association between alcohol consumption and suicide. In countries such as
Sweden the suicide rate is more highly correlated with consumption of alcohol
than in countries such as France (Norstrom,
1995). Indeed, the relationship between alcohol consumption and
the suicide rate is not straightforward. Wine-producing countries with high
alcohol consumption tend to have low suicide rates (e.g. Portugal, France and
Italy). Slovenia is also a wine-producing country, so why does Slovenia have
such high rates of suicide instead of the low rates associated with other
Mediterranean countries? A brief examination of the history of vine-growing in
Slovenia allows a possible explanation in terms of gene-environment
interaction.

Vine-growing in the region, established by the Romans, almost died out
during the time that Slavic and Magyar tribes occupied the area, and wine
production remained limited until the 12th century. One explanation is that
these tribes, whose genetic constitution was not suited to alcohol consumption
and whose descendants also have the highest suicide rates in Europe,
contributed to the genetic make-up of the local people. Once religious and
other environmental factors led to the re-establishment of vine-growing, the
region's inhabitants who were genetically unsuited to alcohol consumption soon
developed the highest rates of both consumption- and alcohol-related
psychiatric disorders. This adverse combination of genetic propensity and high
alcohol consumption led to the high rates of suicide noted in the region
today. Indeed, the suicide rates in parts of the north-east of Slovenia
bordering on Hungary are the same as in Hungary and about twice the rates in
the west of Slovenia (Fig. 2)
(Marušič,
1999).

Regional suicide rate (number per 100 000 per year) distribution in
Slovenia, with 18 out of 60 communes outside the range of the mean (1 s.d.)
suicide rate in Slovenia (5 below and 13 above) in the decade 1985-1994:
[UNK], less than 21.3; [UNK], 21.3-41.1; ▪, more than 41.1.

In addition, alcohol consumption and annual death rates from chronic liver
disease and cirrhosis in Slovenia are among the highest in Europe, and 28% of
completed suicides have a diagnosis of alcohol-related psychiatric problems
(Marušič,
1999). Accordingly, the prevalence of alcohol-related psychiatric
disorders was the best predictor of the regional variation in Slovenian
suicide rates
( Marušič
1999). This supports the theory that there is a malignant
interaction between high alcohol consumption in genetically vulnerable
individuals, leading to high suicide rates.

CONCLUSIONS

We consider that there is sufficient evidence to support the need for more
genetic research into suicide. To date, this has been a relatively
under-investigated area of research. The proposal that there is a genetic
aetiological component to suicidal behaviour does not mean that psychosocial
and other risk factors also are not important. If anything, it would make it
even more necessary to control environmental risk factors in populations of
high genetic risk. However, we contend that unless both genetic as well as
environmental risk factors are taken into account it is unlikely that any
suicide reduction intervention will be effective. A radical rethink of
research strategies is needed and it is our view that molecular genetic
research is an obvious next move, because this may allow targeting of
psychosocial or pharmacotherapeutic interventions at persons of high suicide
risk.